Photo Credits: Cover: David Fleetham/Getty; p. 2: Harcourt; p. 3: Thinkstock/Getty Images; p. 4: Master?le; p. 5: Photodisc Red/Getty Images; p. 6: Harcourt; p. 7: Master?le; p. 8: Photodisc Green/Getty Images; p. 9: Photodisc Green/Getty Images; p. 10: Photodisc Green/Getty Images; p. 11: Harcourt; p. 12: Digital Vision/Getty Images; p. 13: Image Source/Getty Images; p. 14: Hemera Photo-Objects; p. 15: Photodisc Green/Getty Images.Copyright ? by Harcourt, Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the publisher.Requests for permission to make copies of any part of the work should be addressed to School Permissions and Copyrights, Harcourt, Inc., 6277 Sea Harbor Drive, Orlando, Florida 32887-6777. Fax: 407-345-2418.HARCOURT and the Harcourt Logo are trademarks of Harcourt, Inc., registered in the United States of America and/or other jurisdictions.Printed in the United States of AmericaISBN 0-15-362237-71 2 3 4 5 6 7 8 9 10 039 10 09 08 07 06 05Position and Motion ............................................ 2Fast and Slow .................................................... 4Describing Speed ................................................ 6Feeling the Force ................................................ 8Mass and Force ..................................................10Gravity and Weight .............................................12Facts of Friction .................................................14Glossary ...........................................................16Orlando Austin New York San Diego Toronto LondonVisit The Learning Site!www.harcourtschool.comPosition and MotionAre you near a window right now? Are you a few feet away from a friend? Are you sitting to the right or left of your teacher? Everything has a position. Position is the location of an object.Sometimes a position doesn’t change. For instance, the position of your ears on the sides of your head stays the same. Sometimes a position does change, such as when you move from one room to another—or even when you just take a step. When an object
changes position, it’s called motion.
Popcorn explodes with motion! 2This could be a frame of reference for you if the car is moved later.Motion happens in all directions—forward, backward, up, down, straight, and curving. Think of a roller coaster or a bag of popcorn in a microwave. The roller coaster moves forward, up, and down. It also goes straight and curves along a track. Popcorn moves all around inside the bag when it’s being popped.
Let’s think about how we understand the movement of objects. Suppose you look at two photographs taken on the same day. In one photo, a car is parked in front of your house, far away from your driveway. In the other, the same car is closer to your driveway. You know that the car has moved because you know where the driveway is—it is your frame of reference. You compared the position of the
driveway to the position of the car. A frame of reference is something stationary that you compare movement to.
COMPARE AND CONTRAST How would you compare the idea of position to the idea of motion?
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move it
